The objective is understanding of the cellular and molecular mode(s) of action of juvenile hormone (JH), a sesquiterpenoid that regulates metamorphosis and reproductive activity in insects. This is significant for two reasons: (a) as a model for understanding hormonally-regulated development, since JH controls expression of the genome for morphogenesis and cell differentiation; (b) for understanding the mode of action of synthetic JH analogs ("insect growth regulators" which are used as control agents for disease vectors and other pest species. The experimental system, selected for simplicity and accessibility, is the action of JH or an active analog such as methoprene on the fat body tissue of the African migratory locust, where, in the adult female, the synthesis of vitellogenin (Vg; yolk precursor protein) is strictly dependent on JH stimulation. Two locust Vg genes have been cloned and 5' terminal and flanking DNA sequences determined. Assays of the corresponding mRNAs indicate coordinate induction of transcription by JH analog: after a lag time of several hours, the Vg mRNAs rise from zero to become the most abundant messages in the cell. Also observed is a more rapid, more general, lower level stimulation of expression of other genes. A double mode of action of JH on the cells is therefore postulated, with early, non-specific stimulation possibly at the plasma membrane level, followed by specific activation of a few previously silent target genes. The experimental plan includes: (1) completion of cloning and description of several locust genes needed for probes and comparison of regulatory sequences; (2) optimization of conditions for the response of fat body to JH analog in vitro, testing for synergism with other hormones; (3) analysis of the relationships of early events in JH action, by study of their time-course and the effects of specific inhibitors of macromolecular synthesis; (4) development of an insect gene transfer system, by injection of cloned genes in appropriate vectors into early locust embryos and analysis for expression transiently or after integration into the host genome; (5) characterization and purification of the fat body JH receptor protein, and study of binding to specific, potentially regulatory DNA sequences associated with target genes. The results will be considered in relation to current concepts of the molecular actions of hormones, to develop models for JH action in vitellogenesis and the several actions of this hormone in development.